(a) Field of the invention
The present invention relates to an electronic musical instrument, and more particularly it pertains to an electronic musical instrument of the waveshape memory type in which the waveshapes of musical sounds of various natural musical instruments, synthesized musical sounds and/or various effects (totally referred to as musical sounds or tones hereinbelow) are stored in a memory medium, and a particular musical sound waveshape is read out from the memory medium in response to a key depression to generate a desired musical sound.
(B) Description of the prior art
The electronic musical instrument of the waveshape memory type has a clear advantage over that of the waveshape generation type in the following aspects: that musical sounds of high fidelity resembling those of the natural musical instruments can be generated easily since the former, i.e. the waveshape memory type, generates a musical sound by reading the memorized musical sound waveshape whereas the latter, i.e. the waveshape generation type, generates a musical sound by combining the basic tone waveforms such as a group of sinusoidal waveforms. In this specification, the term "waveshape" is used to denote a combination of waveforms, such as those of sinusoidal, saw-tooth, square, and so forth. Standing on the above advantage, various proposals have been made in the past to provide electronic musical instruments of the waveshape memory type, but no electronic musical instruments which have been proposed in the past are able to provide a performance ability competitive with the natural musical instruments while satisfying the practical requirements such as a low manufacturing cost, compact size and easy maintenance.
For example, Japanese Patent Publication No. 41-18291 (U.K. patent application No. 18269/62) discloses an electronic musical instrument of the magnetic tape memory type in which magnetic tapes of finite length are provided, respectively, for the keys of a keyboard of the instrument, and a particular magnetic tape is selected upon the operation of a key to generate a corresponding tone. This prior art electronic musical instrument, however, has many problems to be improved. For example, according to this system, a very complicated driving mechanism is required for immediately bringing the memory initiation point of an assigned magnetic tape corresponding to a depressed key to the position at a reproduction head and also for running the magnetic tape to reproduce a sound without any time delay after the key operation. In particular, in case a particular key is repeatedly operated (depressed and released) within a very short period, it is very difficult, or almost impossible, to bring, at every depression, the memorized wave initiation point of the magnetic tapes to the reproduction head and to feed them to generate the desired tone signals in response to the key operations without any time delay since a magnetic tape is a serial access type memory medium, and since the reproduction of the memory requires physical movement of this tape. Furthermore, a magnetic tape has the drawback that the reproduced tone quality may be deteriorated by the hysteresis distortion, extension and wear of the magnetic tape itself, while it has the advantage that the recording and the reproduction of the memory is easily performed. Yet further, the provision of magnetic tapes in a number equal to that of the keys and the provision of a driving mechanism for these magnetic tapes will make the entire electronic musical instrument large in size and expensive. Thus, the electronic musical instrument of the magnetic tape memory type is unable to satisfy the practical requirements.
U.S. Pat. No. 3,098,889 issued to T. J. Buitkus on July 23, 1963 discloses another example of an electronic musical instrument of the waveshape memory type. In this electronic musical instrument, a multiplicity of coaxial circular memory tracks are formed by coating a photomask on a disk which has an underlie of photo-electric material. Tone waveshapes are recorded in the respective tracks as an optical pattern of opacity. While the disk is rotated, a light beam is irradiated onto a selected track. Then, the intensity of the light beam incident onto the photo-electric material varies with time in accordance with the opacity pattern in the mask, resulting in changes in the resistance or the electromotive force of the photo-electric material on the disk. Thus, an electric tone signal corresponding to the optical pattern of the tone waveshape information recorded in that track is produced. According to such a system, however, there can be produced no tone signal the amplitude and/or pitch of which changes with time since the disk is continuously and constantly rotated and since the memory read-out is commenced at any point in the track and repeatedly continues as long as the beam is being irradiated. In general, a natural musical sound such as the sound of a piano is such that its amplitude and the pitch vary instantaneously from the time a key is depressed up to the time the tone generation is terminated. According to the above U.S. Pat. No. 3,098,889 electronic musical instrument, tone waveshape is reproduced from an arbitrary point in an endless track, and therefore the tone waveshape that can be recorded in each track is limited to a burst waveshape, and accordingly time-dependent variations of the amplitude and the pitch of the tone as those of the natural musical sound cannot be provided.
As has been described above, conventional electronic musical instruments of the waveshape memory type which have been provided in the past have many problems that require to be improved. Such problems can be ascribed to the inherent property of the recording medium for recording the tone waveshape. An improvement of the read-out speed of the tone waveshape can be achieved by the employment of the generally known high speed random access memories such as core memory, semiconductor memory, and the like. In an electronic musical instrument, however, a considerably large memory capacity is required for recording the tone waveshape (for example, each 5 ms sample values for 4 sec single tone generation amount to 800 sample values, and 88 kinds of tone will require over 70 thousands sample values). When a core memory of such memory capacity with necessary terminal devices such as read-write circuit is employed, the result will be that the fabricated electronic musical instrument will be large in size and expensive. In particular, the problem in the manufacturing cost almost prohibits the use of such core memory.